1. Field of the Invention
The present invention relates to a method of fabricating a bonding structure, and more particularly to a method of fabricating a bonding structure using a non-conductive adhesive layer as a bonding medium.
2. Description of Related Art
With rapid advancement in the liquid crystal display (LCD) technology, the new generation of LCDs with advantages of high brightness, wide viewing angle, fast responding speed, high resolution, and full-colors has been developing. The quality of the displayed images is determined by structures of liquid crystal molecules, physical characteristics of pixel electrodes, color filters, a process of manufacturing thin film transistors (TFTs), alignment layers, a material of a sealant, post-end packaging technologies, and so forth. With the demand for high resolution LCDs and for light and compact electronic devices, the packaging technology evolving from a chip-on-board (COB) bonding technology to a tape-automated-bonding (TAB) technology is now advanced to a fine-pitch chip-on-glass (COG) bonding technology.
In the most common COG bonding process uses an anisotropic conductive film as a medium through which a driver IC and a LCD panel are electrically connected to each other. First of all, the anisotropic conductive film is disposed on the driver IC bonding region of the LCD. Then, the driver IC is compressed onto the anisotropic conductive film through a process of heating and pressurizing, such that the bumps on the driver IC and the bonding pads on the LCD panel are electrically conducted through conductive particles of the anisotropic conductive film. However, when a pitch between two adjoining bumps is relatively small, the conductive particles of the anisotropic conductive film easily result in short circuit of the bumps, thus limiting the miniaturization of the gap between the chip and the glass.
In order to solve the aforementioned problem, a non-conductive film (NCF) is proposed to replace said anisotropic conductive film, so as to meet the requirement of ultra high-density bonding. Nevertheless, there is a significant difference between the coefficient of thermal expansion (CTE) of the NCF and that of the chip and the glass substrate. Accordingly, after the COG bonding process is completed, the chip and the glass substrate are prone to micro-delamination, and structural micro-cracks or structural micro voids further pose a great impact on reliability of contacts.
FIG. 1 is a schematic cross-sectional view illustrating a conventional bonding structure. Please refer to FIG. 1. The bonding structure 100 mainly includes a first substrate 110 and a second substrate 120. The first substrate 110 includes a plurality of first bonding pads 112 and bumps 114 disposed thereon. Likewise, the second substrate 120 includes a plurality of second bonding pads 122 and bumps 124 disposed thereon. The second bonding pads 122 are opposite to the first bonding pads 112. As a reflow process is performed on the substrates, the bumps 114 and 124 are fused together, such that the first substrate 110 is electrically connected to the second substrate 120. One of the technical features of the bonding structure 100 lies in that a metal layer 116, 126 with a high melting point is disposed in the metal layer below the bumps 114 and 124. The metal layer 116, 126 is composed of aurum (Au), for example. Thereby, the unmelted metal layer 116, 126 provides a desirable support during the reflow process.
FIGS. 2A and 2B are schematic cross-sectional views illustrating a conventional COG bonding process. First, referring to FIG. 2A, a substrate 210 and a chip 220 opposite thereto are provided. Several corresponding bumps 212, 222 are then disposed on the glass substrate 210 and the chip 220. In addition, several stud bumps 224 with a high melting point metal are further disposed on the chip 220. The stud bumps 224 are composed of Au, for example. Please refer to FIG. 2B. As the reflow process is carried out, the bumps 212 and 222 fuse together, such that the substrate 210 is electrically connected to the chip 220. Moreover, during the reflow process, the stud bumps 224 is adapted to support the whole chip 220, so as to maintain the gap between the substrate 210 and the chip 220.
Furthermore, a “bonding structure with compliant bumps” is disclosed in U.S. Pat. No. 6,972,490. Referring to FIG. 3, the bonding structure 300 mainly includes a first substrate 310, a second substrate 320, and a non-conductive adhesive layer 330 sandwiched between the first and the second substrates. A compliant bump 314 is respectively disposed on each of the metal bonding pads 312 on the first substrate 310, such that the metal bonding pads 312 are electrically connected to the metal bonding pads 322 on the second substrate 320 through the compliant bump 314. One of the technical features of the bonding structure 300 lies in that several stoppers 316 are simultaneously formed while several tapered bumps 314a are formed within the compliant bumps 314. Thereby, the stoppers 316 are used to prevent the compliant bumps 314 from cracking due to overpressure in the COG bonding process, thus leading to conductance of the contacts.